As of 30 September 1996, ten cases of vivax malaria were diagnosed and treated at the 121st General Hospital at Yongsan Garrison, Seoul, Korea (see map on page 3). The first case, a Korean soldier assigned to the United Nations Command (UNC) Security Battalion Joint Security Area (JSA) at Panmunjom, was admitted to the 121st General Hospital on 20 June. On 28 June, an investigation by preventive medicine (PM) specialists from the 5th Medical Detachment (Entomology) and the 168th Medical Battalion (AS) revealed a significant mosquito problem at the site. In late June and mid-July, two additional cases were diagnosed in Korean soldiers assigned to the UNC Security Battalion at Panmunjom. Primary health care providers near the Demilitarized Zone (DMZ) were alerted to the vivax malaria threat. In late July, the summer monsoons produced heavy flooding near the DMZ. No additional cases were diagnosed during late July or early August. During the last week of August, two cases were diagnosed in US soldiers: one was assigned to the JSA at Panmunjom; the other was a PM technician who had conducted human bite mosquito collections at the JSA. During the first week of September, five US soldiers were admitted to the 121st General Hospital with vivax malaria. All had trained north of the Imjin River near the JSA. In response, the USFK Surgeon recommended that soldiers assigned or training north of the Imjin River take chloroquine for chemoprophylaxis and primaquine for terminal prophylaxis at the end of their exposure. The USFK Blood Center was notified to ensure that the blood supply was adequately protected. On 6 September, the 18th MEDCOM Commander requested epidemiologic consultation (EPICON) to assist in developing a long term (3-5 year) strategy for malaria prevention. A multidisciplinary team representing USACHPPM, WRAIR, and the Fort Drum medical activity traveled to Korea in response to the request.